How to handle fish waste emanating from coastal fish farms has remained a problematic issue. Stanford University researchers have now developed a system to figure out suitable locations for farm pens to reduce waste plumes’ ability to reach coastlines.

“For many years, people have assumed that because of the ocean's size, because of the energy in its currents, that any substance you introduced into the ocean would quickly be diluted into concentrations that were barely detectable," commented Jeff Koseff, professor of civil and environmental engineering.

To tackle the issue, Koseff and Roz Naylor, a Stanford professor of environmental Earth system science, plus Oliver Fringer, assistant professor of civil and environmental engineering, and a team of colleagues devised a computational model that allows researchers to foretell where the waste matter from coastal fish farms would disperse in the water. The simulation calculates variables including tides, currents, the Earth’s rotation and the physical structure of the pens.

"We discovered that the state of the natural environment around fish pens can dramatically affect how far waste plumes travel from the source," Koseff told. "This suggests that we should not simply assume 'dilution is the solution' for aquaculture pollution."

"These plumes actually remain quite coherent at very long distances from the source and could become a major pollution problem in coastal regions," he continued.

Naylor and Koseff believe the model can be used to select future farm sites in order to minimise the amount of faeces and uneaten food that reaches coasts.

The model will demonstrate that some locations where fish farms were already built are not appropriate, but that the aquaculture industry may respond positively, as this new knowledge will help the sector coexist more comfortably with other users of coastal waters.

"A lot of the industry people that I have talked to are not working against the environment, they are really trying to make aquaculture work, and this would provide a useful tool for them," she reasoned.

Legislation is currently being drafted at the state and federal levels, making the team’s findings timely as well as useful, Naylor noted.

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